Photoelectric conversion element

ABSTRACT

In a photoelectric transfer device having a semiconductor electrode composed of semiconductor nanoparticles and an electrolyte layer between a pair of transparent conductive substrates, a transparent conductive substrate at the light-receiving side is made by stacking a transparent substrate, conductive wiring layer and a metal oxide layer in order from the light-receiving side and having sheet resistance equal to or lower than 10 Ω/□. The metal oxide layer is made of an In—Sn composite oxide, SnO 2 , TiO 2 , ZnO, or the like.

TECHNICAL FIELD

The present invention relates to a photoelectric transfer deviceespecially suitable for application to wet solar cells.

BACKGROUND ART

It is generally recognized that the use of fossil fuel such as coal andpetroleum as energy sources invites global warming by resultant carbondioxide. The use of atomic energy accompanies the risk of contaminationby radioactive rays. Currently under various discussions on theenvironmental issues, dependence upon these kinds of energy isundesirable.

On the other hand, solar cells, which are photoelectric transfer devicesfor converting sunlight to electric energy, use sunlight as their energyresources, and they produce only a small adverse effect to the globalenvironment. Therefore, wider distribution of solar cells isanticipated.

Although there are various materials of solar cells, a number of solarcells using silicon are commercially available. These solar cells areroughly classified to crystalline silicon solar cells using singlecrystal or polycrystal and amorphous silicon solar cells. Inconventional solar cells, single crystal silicon or polycrystal silicon,i.e. crystalline silicon, has been used often.

In crystalline silicon solar cells, photoelectric transfer efficiency,which represents the performance of converting light (sun) energy toelectrical energy, is higher than that of amorphous silicon solar cells.However, since crystalline silicon solar cells need much energy and timefor crystal growth, they are disadvantageous from the viewpoint of theircosts.

Amorphous silicon solar cells are advantageous in higher lightabsorption, wider selectable range of substrates and easier enlargementof the scale. However, photoelectric transfer efficiency of amorphoussilicon solar cells is lower than that of crystalline silicon solarcells. Furthermore, although amorphous silicon solar cells are higher inproductivity than crystalline silicon solar cells, they need anevacuation process for the manufacture. Therefore, the burden related tofacilities for fabrication of crystalline silicon solar cells is stillheavy.

On the other hand, there have been long researches in solar cells usingorganic materials toward more cost reduction of solar cells. However,they exhibit as low photoelectric transfer coefficient as 1%, andinvolve difficulties in durability as well.

Under the circumstances, an inexpensive solar cell using dye-sensitizedporous semiconductor particles was introduced in Nature 353, p. 737,1991. This is a wet solar cell, i.e. an electrochemical photocell whosephoto electrode is a titanium oxide porous film spectrally sensitized byusing ruthenium complex as a sensitizing dye. This solar cell hasadvantages in that inexpensive oxide semiconductors such as titaniumoxide can be used; light absorption of the sensitizing dye ranges widelyover the visible wavelength up to 800 nm; and quantum efficiency of thephotoelectric transfer is high enough to realize high energy conversionefficiency. Moreover, because the solar cell does not need a process ina vacuum for its manufacture, it does not require bulky facilities orequipment.

If this solar cell is large-scaled (widened in area), it is difficult torealize a favorable photoelectric transfer efficiency by using acommercially available resistant-to-oxidization transparent conductivesubstrate because it has a high sheet resistance and causes a loss offill factor. Therefore, to make a large-scale solar cell, it isnecessary to take measures for patterning highly conductive metal orcarbon wiring on the substrate to reduce the sheet resistance of thetransparent conductive substrate.

In this solar cell, however, its electrolyte contains iodine and/orother halogens. Therefore, it involves the problem of dissolution ordisconnection of wirings by corrosion and breakdown of wirings bydissolution of base metals. Thus, the solar cell seriously deterioratesin characteristics with time. Even when a metal excellent in corrosionresistance is used as the wiring material, its direct contact with thewirings and the electrolyte causes and retains the problem of so-calledreverse electron transfer where electrons injected into thesemiconductor and reaching the wirings deoxidize the electrolyte beforeflowing out to the external circuit.

It is therefore an object of the invention to provide a photoelectrictransfer device free from reverse electron transfer reaction, excellentin durability and having high photoelectric transfer efficiency.

DISCLOSURE OF INVENTION

To accomplish the above object, there is provided a photoelectrictransfer device characterized in the use of a transparent conductivesubstrate made by stacking a transparent substrate, a conductive wiringlayer and a protective layer in order from a light-receiving side andhaving sheet resistance equal to or less than 10 Ω/□.

Preferably, plural lines of the conductive wiring layer are provided,and at least one line of the conductive wiring layer is bonded to acollector portion of the photoelectric transfer device to enhance thecollecting efficiency. In the present invention, the term “transparent”specifies that transmittance of visible to near-infrared light havingwavelengths of 400-1200 nm is 10% or more in a local or entire area. Theconductive wiring layer is preferably made of a material exhibiting highelectronic conductivity, which is more preferably stableelectrochemically. More specifically, here is preferably used, althoughnot limitative, a conductive material (simplex metal, alloy, etc.)containing at least one element selected from the group consisting ofPt, Au, Ru, Os, Ti, Ni, Cr, Cu, Ag, Pd, In, Zn, Mo, Al and C. Thicknessof the conductive wiring layer made of such a material is notlimitative. However, the thicker the layer, higher electron transferproperty can be realized. However, if the layer is too thick, surfaceroughness will become large and will make it difficult to deposit theprotective layer uniformly. In this case, the adhesiveness of theprotective layer will seriously degrade. Therefore, there is apreferable thickness for the conductive wiring layer. Although there isa difference in sheet resistance attained depending upon the nature ofthe material, thickness of the conductive wiring layer is typically10-10000 nm, or more preferably 50-5000 nm. There is no speciallimitation regarding the coverage of the conductive wiring layerrelative to the photo detective surface of the light photoelectrictransfer device. However, the coverage is preferably within 0.01%-50%.If the coverage is too large, detected light cannot pass throughsufficiently. Therefore, the coverage is more preferably 0.1%-20%. Widthof each conductive wiring layer and distance between adjacent conductivewiring layers are not limitative. The wider the width, and the narrowerthe distance, the electron transfer property will be enhanced. However,if the width is too wide, or if the distance is too narrow,transmittance of incident light will decrease. Therefore, there arepreferable values for them. Width of each conductive wiring layer istypically 1-1000 μm, and preferably 10-500 μm. Distance between adjacentconductive wiring layers is typically 0.1-100 mm, and preferably 1-50mm. Any method may be used to form the conductive wiring layers on thetransparent substrate among vapor deposition, ion plating, sputtering,CVD, plating, dispersion coating, dipping, spinner technique, and otherknown techniques. To enhance the adhesiveness of the conductive wiringlayers to the transparent substrate, a more adhesive base material maybe interposed between the conductive wiring layers and the transparentelectrode. The conductive wiring layers may be patterned by any methodamong laser cutting, etching, lift-off, and other known techniques.

The protective layer has the role of blocking the conductive wiringlayers from the electrolyte and preventing reverse electron transfer andcorrosion of the conductive wiring layers. The protective layer ispreferably excellent in electron transfer (not only by normal electricconduction but also by tunneling) and transparent. Subject to theserequirements, the protective layer may be made of any material, and mayhave either a single-layered structure or a multi-layered structureincluding at least two layers made of different materials. A metal oxidelayer is typically used as the protective layer, but a metal nitridelayer such as TiN, WN, or the like, may be used as well. Examples ofmetal oxides are In—Sn composite oxides (ITO), SnO₂ (including thosedoped with fluorine or the like), TiO₂, ZnO, and others. Although theseare not limitative materials, at least one of them is preferablycontained. There are no special restrictions regarding the thickness ofthe metal oxide layer. However, if the metal oxide layer is too thin, itwill not be able to block the conductive wiring layers from theelectrolyte effectively. If the metal oxide layer is too thick, thetransmittance will decrease. In this sense, there is a preferable valueof the thickness. The thickness is typically 1-5000 nm, and preferably10-1000 nm. To enhance the resistance to oxidization, some of the abovemetal oxides may be stacked, if necessary.

The transparent substrate may be made of any material among various basematerials provided it is transparent. The transparent substrate ispreferably good in blockage of moisture and gas intruding from theexterior of the photoelectric transfer device, resistance to thesolvent, weatherability, and so on. Candidates include transparentinorganic substrates of quartz, glass, or the like, transparent plasticsubstrates of polyethylene terephthalate, polyethylene naphthalate,polycarbonate, polyethylene, polypropylene, polyphenylene sulfide,polyvinylidene fluoride, tetraacetyl cellulose, phenoxy bromide, aramid,polyimide, polystyrene, polyarylate, polysulfone, polyolefin, and soforth. Although they are not restrictive, substrates exhibiting hightransmittance to visible light are especially preferable. Taking easierworkability and lighter weight into account, transparent plasticsubstrates are preferable candidates. There are no specific limitationson the thickness of the transparent substrate. The thickness isdetermined as desired, depending upon the light transmittance, blockingcapability between the interior and the exterior of the photoelectrictransfer element, and other factors.

Usable materials of semiconductor nanoparticles are elementarysemiconductors represented by silicon, various compound semiconductors,compounds having a perovskite structure, and so forth. Thesesemiconductors are preferably n-type semiconductors in which electronsin the conduction band behave as carriers and provide an anode currentwhen excited by light. Examples of such semiconductors are metal oxidessuch as TiO₂, ZnO, WO₃, Nb₂O₃, TiSrO₂ and SnO₂. Among them, TiO₂ isespecially desirable. However, usable semiconductors are not limited tothose suggested above, and two or more of them may be used in mixture.

The semiconductor layer (semiconductor electrode) composed ofsemiconductor nanoparticles may be made by any technique. However, whenphysical properties, convenience, manufacturing costs, etc. are takeninto consideration, wet film-forming methods are preferable. Especiallyrecommended is a method of preparing a paste prepared by uniformlydispersing semiconductor nanoparticles in powder or sol into water orother solvent coating it on the transparent conductive substrate. Anycoating method may be used here for example among dipping, spraying,wire bar technique, spin coating, roller coating blade coating, gravurecoating and other known techniques. Alternatively, any wet printingmethod can be used for example among relief printing, offset printing,gravure printing, intaglio printing, rubber plate printing, screenprinting, and so forth. In the case where crystalline titanium oxide isused as the material of the semiconductor nanoparticles, it preferablyhas an anatase crystal structure from the photocatalytic standpoint.Anatase-type titanium may be commercially available powder, sol orslurry, or may be uniformed in grain size by a known technique such ashydrolyzing titanium oxide alcoxide. In the case where commerciallyavailable powder is used, secondary agglomeration of particles ispreferably prevented. For this purpose, the powder preferably undergoesgrinding of particles in a mortar or a ball mill upon preparation of thecoating liquid. In this process, to prevent that particles once releasedfrom secondary agglomeration agglomerate again, acetyl acetone,hydrochloric acid, nitric acid, surfactant, chelating agent, or thelike, may be added. Furthermore, to enhance the viscosity, anythickening agent among polymers such as polyethylene oxide and polyvinylalcohol or cellulose-based viscosity improvers, for example, may beadded.

There are no special restrictions regarding the grain size of thesemiconductor nanoparticles. However, the grain size is preferably 1-200nm and more preferably 5-100 nm in average grain size of primaryparticles. It is also possible to mix semiconductor nanoparticles havinga larger grain size with the semiconductor nanoparticles having theaforementioned average grain size to have the semiconductornanoparticles having the larger grain size to scatter incident light,thereby enhancing the quantum yield. In this case, the average grainsize of the semiconductor nanoparticles to be added is preferably 20-500nm.

The semiconductor layer composed of semiconductor nanoparticlespreferably has a surface area large enough to absorb as many dyeparticles as possible. For this purpose, the surface area of thesemiconductor nanoparticle layer coated on the support structure ispreferably ten times or more, or more preferably 100 times or more, ofthe projected area. Although there is no ceiling for the surface area,it is normally 1000 times or so. In general, as the semiconductornanoparticle layer increases its thickness, its light-capturing rateincreases because of an increase of retained due particles per unitprojected area. However, because injected electrons must travel longerto diffuse, the loss by charge recombination also increases. Therefore,there is a preferable range of thickness for the semiconductornanoparticle layer. It is generally 0.1-100 μm, more preferably 1-50 μm,and most preferably 3-30 μm. Semiconductor nanoparticles are preferablybaked after being coated on the support structure to make electricalcontact with each other and to improve the strength of the film and theadhesiveness with the substrate. There are no special restrictions onthe range of calcination temperature. However, if the temperature is toohigh, it undesirably increases the substrate resistance and may resultin melting the substrate. Therefore, the temperature is normally 40-700°C. and more preferably 40-650° C. The calcination time is normally from10 minutes to 10 hours approximately, although not limitative. Aftercalcination, for purposes of increasing the surface area ofsemiconductor particles, removing impurities from the semiconductornanoparticle layer and enhancing the efficiency of electron injectionfrom the dye into semiconductor nanoparticles, the semiconductornanoparticle layer may undergo chemical plating using water solution oftitanium tetrachloride or electrochemical plating using water solutionof titanium trichloride. In addition, a conduction-assisting agent maybe added to reduce the impedance of the semiconductor nanoparticlelayer. In case a plastic substrate is used as the support structure ofthe transparent conductive layer, a paste containing a bonding agent andcontaining semiconductor nanoparticles dispersed therein may be formed(coated) on the substrate such that the semiconductor nanoparticles arebonded to the substrate under pressure from a heating press at 50-120°C., for example.

Any dye, having a sensitizing function, may be employed to be retainedby the semiconductor nanoparticles. Examples of the dye arexanthene-based dyes such as rhodamine B, rose bengal, eosin andErythrocin; cyanine-based dyes such as quinocyanine and cryptocyanine;basic dyes such as phenosafranine, Capri blue, thiocin and methyleneblue; porphyrin-based compounds such as chlorophyll, zinc porphyrin andmagnesium porphyrin; azo dyes; phthalocyanine compounds; coumarin-basedcompounds; ruthenium (Ru) bipyridine complex compound;anthraquinone-based dyes; and polycyclic quinone-based dyes. Among them,Ru bipyridine complex compound is preferable because of its high quantumyield. However, without being limited to it, those dyes can be usedalone or as a mixture of two or more kinds of them.

The dye may be retained by the semiconductor nanoparticle layer in anyform or manner. For example, a typical method dissolves any of theabove-mentioned dyes in a solution such as alcohols, nitriles,nitromethane, halogenated hydrocarbon, ethers, dimethyl sulfoxide,amides, N-methylpyrrolidone, 1,3-dimethyl imidazolidinone, 3-methyloxazolidinone, esters, carbonic acid esters, ketones, hydrocarbon,water, and so on; and next immerses the semiconductor nanoparticle layertherein, or coats the dye solution on the semiconductor nanoparticlelayer. In this case, the quantity of dye molecules to be retained by thesemiconductor nanoparticles is preferably in the range of 1-1000molecules, and more preferably in the range of 1-100 molecules. If farexcessive dye molecules are retained by semiconductor nanoparticles,electrons excited by light energy are not injected into semiconductornanoparticles and rather deoxidize the electrolyte. Thus, excessive dyemolecules rather invite energy loss. Therefore, it is ideal that asingle dye molecule is retained by a single semiconductor nanoparticle,and the temperature and pressure for retainment can be changed ifnecessary. For the purpose of reducing association of dye particles,carboxylic acid such as deoxycholic acid may be added as well. It isalso possible to use an ultraviolet absorbent together.

For the purpose of removing excessively retained dye particles, thesemiconductor nanoparticle layer may undergo surface treatment using akind of amine after the dye particles absorb. Examples of amine systemsubstances are pyridine, 4-tert-butyl pyridine, polyvinyl pyridine, andso on. If they are liquids, they can be used either directly or in formof solution in an organic solvent.

Any conductive material may be used as the counter electrode. Even aninsulating material can be used in combination with a conductive layerformed to face the semiconductor electrode. However, the material usedas the electrode is preferably stable in electrochemical properties. Inthis sense, platinum, gold, carbon, or the like, is preferably used. Toenhance the oxidation-reduction catalytic effect, one side of thecounter electrode opposed to the semiconductor electrode preferably hasa minute structure increased in surface area. For example, in case ofplatinum, it is preferably in the state of platinum black. In case ofcarbon, it is preferably in a porous state. Such a platinum black statecan be made by anodic oxidation, chloroplatinic treatment, or the like.Porous carbon can be made by sintering of carbon nanoparticles,calcination of organic polymer, or the like. Alternatively, it is alsoacceptable to make wirings of a metal having a high oxidation-reductioncatalytic effect such as platinum on the transparent conductivesubstrate, or treat the surface by chloroplatinic treatment, to use itas a transparent counter electrode.

The electrolyte may be a combination of iodine (I₂) and metal iodide ororganic iodide, or a combination of boron (Br₂) and metal boride ororganic boride. Also usable are metal chains such as ferrocyanic acidsalt/ferricyanic acid salt and ferrocene/ferricynium ions, sulfurcompounds such as sodium polysulfide and alkylthiol/alkyldisulfide,viologen dyes, hydroquinone/quinone, and so forth. Preferable cations ofthe above metal compounds are Li, Na, K, Mg, Ca, Cs, or the like, andpreferable cations of the above organic compounds are quaternaryammonium compounds such as kinds of tetraalkyl ammoniums, pyridiniums,imidazoliums, and so forth. However, without being limited to them,cations may be combinations of two or more kinds of them. Among them,electrolytes combining I₂ and quaternary ammonium compounds such as LiI,NaI or imidazolium iodides, or the like, are desirable. Concentration ofthe electrolyte salt is preferably 0.05-5 M, or more preferably 0.2-1 M,with respect to the solvent. Concentration of I₂ and Br₂ is preferably0.0005-1 M, or more preferably 0.001-0.1 M. To improve the open-circuitvoltage and short-circuit current, various kinds of additives such as4-tert-butyl pyridine, carboxylic acid, or the like, may be added.

The solvent composing the electrolyte composite may be selected fromwater, alcohols, ethers, esters, carbonic acid esters, lactones,carboxylic acid esters, phosphoric triesters, heterocyclic compounds,nitriles, ketones, amides, nitromethane, halogenated hydrocarbon,dimethyl sulfoxide, sulforan, N-methyl-pyrrolidone, 1,3-dimethylimidazolidinone, 3-methyl oxazolidinone, hydrocarbon, and so forth, eachalone, or in combination of two or more kinds of them. As the solvent,room-temperature ionic liquids of quaternary ammonium salts of tetraalkyl system, pyridinium system or imidazolium system are usable aswell.

To reduce liquid leakage of the photoelectric device and vaporization ofthe electrolyte, it is also possible to dissolve a gelatinizer, polymer,cross-linking monomer, or the like, into the electrolyte composite toform a gel electrolyte. As to the ratio of the electrolyte compositerelative and the gel matrix, if the electrolyte composite is abundant,the ion conductivity gets higher, but the mechanical strength decreases.In contrast, if the electrolyte composite is too scarce, the mechanicalstrength increases, but the ion conductivity decreases. Therefore, theelectrolyte composite is preferably 50-99 wt %, and more preferably80-97 wt %. It is also possible to realize a fully solid photoelectrictransfer device by dissolving the electrolyte and a plasticizer into apolymer and removing the plasticizer by vaporization.

The photoelectric transfer device may be manufactured by any method. Forexample, the electrolyte composite may be in liquid form or may begelatinized inside the photoelectric transfer device. In case theelectrolyte is in liquid form before being introduced, the semiconductorelectrode retaining the dye and the counter electrode are put togetherface to face, and a part of the substrate not having the semiconductorelectrode is sealed such that these two electrodes do not contact. Thegap between the semiconductor electrode and the counter electrode may bedetermined appropriately. However, it is normally 1-100 μm, or morepreferably 1-50 μm. If the distance between the electrodes is too long,light current decreases due to a decrease of the conductivity. Anymethod can be used for the sealing. However, it is preferable to use amaterial excellent in resistance to light, electrical insulation anddamp-proof capability. For this purpose, various methods and materialsare usable, such as epoxy resins, ultraviolet-setting resins, acrylicadhesives, EVA (ethylene vinyl acetate), ionomer resins, ceramics, heatseal films, and so forth. An inlet required for introducing the solutionof the electrolyte composite may be mad at any position except theposition of the dye-retained semiconductor electrode and the counterelectrode. The solution may be introduced by any method. However, thesolution is preferably introduced inside the cell already sealed andhaving the solution inlet. In this case, it is an easy way to pour dropsof the solution into the inlet and introduce it inside by capillaryphenomenon. If desired, introduction of the solution may be conductedunder reduced pressure or heat. After the solution is fully introduced,an extra amount of the solution remaining in the inlet is removed, andthe inlet is sealed. Any method may be used for the sealing of theinlet. If necessary, however, a glass plate or a plastic substrate, forexample, may be bonded with a sealing agent to seal the inlet. In thecase of gel electrolytes and fully solid electrolytes using polymers orthe like, the polymer solution containing an electrolyte composite and aplasticizer is removed by vaporization by a casting method from abovethe dye-retained semiconductor electrode. After the plasticizer is fullyremoved, the inlet is sealed in the above manner. This sealing ispreferably conducted in a vacuum sealer, or the like, providing aninactive gas atmosphere or a reduced pressure. After the sealing, heator pressure may be applied, if necessary to impregnate the semiconductornanoparticle layer with the electrolyte.

The photoelectric transfer device may be fabricated in various formssuitable for their use, without being limited to specific forms.

According to the invention having the above construction, since it usesthe transparent conductive substrate made by stacking the transparentsubstrate, conductive wiring layer and protective layer such as a metaloxide layer in order from the light-receiving side and having sheetresistance equal to or less than 10 Ω/□, in which the conductive wiringlayer and the electrolyte are not in direct contact, it not onlyprevents reverse electron transfer reaction but also prevents corrosionof the conductive wiring layer. Thus, the invention can realize aphotoelectric transfer device excellent in durability and photoelectrictransfer efficiency.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view showing a dye-sensitized wetphotoelectric transfer device according to an embodiment of theinvention;

FIG. 2 is a cross-sectional view of the part of the conductive wiringlayer in the dye-sensitized wet photoelectric transfer device accordingto the first embodiment of the invention; and

FIG. 3 is a plan view of a substantial part of the dye-sensitized wetphotoelectric transfer device according to the first embodiment of theinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the invention will now be explained below withreference to the drawings.

FIG. 1 shows a dye-sensitized wet photoelectric transfer deviceaccording to an embodiment of the invention.

As shown in FIG. 1, in the dye-sensitized wet photoelectric transferdevice, a transparent substrate 1, having a semiconductor nanoparticlelayer 3 (semiconductor electrode) retaining a sensitizing dye on itsmajor surface via a semiconductor wiring layer/metal oxide layer 2, anda transparent conductive substrate 4, having a platinum or platinumcatalyst layer 5 on its major surface, are put together such that thesemiconductor nanoparticle layer 3 and the platinum or platinum catalystlayer 5 face to each other via a predetermined distance. In a spacebetween them, an electrolyte layer (electrolytic solution) 6 isenclosed.

FIG. 2 shows details of the conductive wiring layer/metal oxide layer 2stacked on the major surface of the transparent substrate 1. As shown inFIG. 2, the transparent substrate 1, conductive wiring layer 2 a andmetal oxide layer 2 b are stacked in order from the light-receiving sideto form the transparent conductive substrate having sheet resistanceequal to or less than 10 Ω/□. The conductive wiring layer 2 a is fullycovered by the metal oxide layer 2 integrally deposited on the entiresubstrate surface.

FIG. 3 shows a plan view (projected figure) of the dye-sensitized wetphotoelectric transfer device, taken from the light-receiving side ofthe transparent conductive substrate. The conductive wiring layer 2 a isconnected to a collector portion 7.

Materials of the transparent substrates 1, conductive wiring layer 2 a,metal oxide layer 2 b, semiconductor nanoparticle layer 3, transparentconductive substrate 4 and electrolyte layer 6 may be selectedappropriately from the materials already introduced herein.

Next explained is a manufacturing method of the dye-sensitized wetphotoelectric transfer device.

First prepared is the transparent substrate 1. Next, the conductivewiring layer 2 a of a predetermined pattern is formed on the transparentsubstrate 1 by lithography, lift-off, or the like. Thereafter, the metaloxide layer 2 b is formed on the entire surface of the transparentsubstrate 1 to cover the conductive wiring layer 2 a. After that, apaste with dispersed semiconductor nanoparticles is coated on the metaloxide layer 2 b to a predetermined gap (thickness). Then, thesemiconductor nanoparticles are sintered by heat of a predeterminedtemperature for a predetermined time. As a result, the semiconductornanoparticle layer 3 is formed on the metal oxide layer 2 b. After that,the semiconductor nanoparticle layer 3 is immersed into a dye solution,for example, to have it retain the dye.

On the other hand, the transparent conductive substrate 4 is preparedseparately, and a platinum or platinum catalyst layer 5 is formedthereon.

In the next step, the transparent substrate 1, having the conductivewiring layer 2 a, metal oxide layer 2 b and dye-retained semiconductornanoparticle layer 3 thereon, and the transparent conductive substrate 4are put together such that the semiconductor nanoparticle layer 3 andthe platinum or platinum catalyst layer 5 face to each other via adistance of 1-100 μm or preferably 1-50 μm and a space for receiving theelectrolyte layer 6 by using a predetermined sealing member. Then, theelectrolyte layer 6 is introduced into the space through an inletpreviously made, and the inlet is closed thereafter. As a result, thedye-sensitized wet photoelectric transfer device is completed.

Next explained are operations of the dye-sensitized wet photoelectrictransfer device.

Incident light entering from and passing through the transparentsubstrate 1 excites the sensitizing dye retained on the surface of thesemiconductor nanoparticle layer 3, and generates electrons. Theelectrons are quickly delivered from the sensitizing dye to thesemiconductor nanoparticles of the semiconductor nanoparticle layer 3.On the other hand, the sensitizing dye having lost the electrons againreceives electrons from ions of the electrolyte layer 6, and moleculeshaving delivered the electrons again receive electrons at the platinumor platinum catalyst layer i5 of the counter electrode. Through thisseries of actions, electromotive force is generated between thetransparent conductive substrate, which is composed of the sequentiallystacked transparent substrate 1, conductive wiring layer 2 a and metaloxide layer 2 b and electrically connected to the semiconductor particlelayer 3, and the transparent conductive substrate 4 electricallyconnected to the platinum or platinum catalyst layer 5. Photoelectrictransfer takes place in this manner.

As explained above, according to this embodiment, since it uses thetransparent conductive substrate made by stacking the transparentsubstrate 1, conductive wiring layer 2 a and metal oxide layer 2 b fromthe light-receiving side, and thereby prevents direct contact betweenthe conductive wiring layer 2 a and the electrolyte 6 in order, it canprevent not only the reverse electron transfer reaction but alsocorrosion of the conductive wiring layer 2 a. Thus, the embodiment canrealize the dye-sensitized wet photoelectric transfer device, inparticular, a dye-sensitized wet solar cell, which is excellent indurability and photoelectric transfer efficiency.

Some practical examples of the dye-sensitized wet photoelectric transferdevice are explained below. Conditions of the examples are shown inTable 1 together with conditions of comparative examples. In addition,results of measurement of the practical examples are shown in Table 2together with results of measurement of the comparative examples. TABLE1 Conductive wiring Layer Metal Oxide Layer Example 1 Ru 4500Δ/Cr 500ΔITO 4500Δ/SnO₂ 500Δ Example 2 Ru 4500Δ/Cr 500Δ FTO 5000Δ Example 3 Ru4500Δ/Cr 500Δ ITO 4500Δ/TiO₂ 200Δ Example 4 Ru 4500Δ/Cr 500Δ ITO4500Δ/ZnO₂ 200Δ Example 5 Pt 4500Δ/Cr 500Δ ITO 4500Δ/SnO₂ 500Δ Example 6Au 4500Δ/Cr 500Δ ITO 4500Δ/SnO₂ 500Δ Example 7 Os 4500Δ/Cr 500Δ ITO4500Δ/SnO₂ 500Δ Example 8 Ti 5000Δ ITO 4500Δ/SnO₂ 500Δ Example 9 Ni4500Δ/Cr 500Δ ITO 4500Δ/SnO₂ 500Δ Example 10 Cr 5000Δ ITO 4500Δ/SnO₂500Δ Example 11 Cu 4500Δ/Cr 500Δ ITO 4500Δ/SnO₂ 500Δ Example 12 Ag4500Δ/Cr 500Δ ITO 4500Δ/SnO₂ 500Δ Example 13 Pd 4500Δ/Cr 500Δ ITO4500Δ/SnO₂ 500Δ Example 14 In 4500Δ/Cr 500Δ ITO 4500Δ/SnO₂ 500Δ Example15 Zn 4500Δ/Cr 500Δ ITO 4500Δ/SnO₂ 500Δ Example 16 Mo 4500Δ/Cr 500Δ ITO4500Δ/SnO₂ 500Δ Example 17 Al 5000Δ ITO 4500Δ/SnO₂ 500Δ Example 18  C4500Δ/Cr 500Δ ITO 4500Δ/SnO₂ 500Δ Comparative 1 Ru 4500Δ/Cr 500Δ NoneComparative 2 Pt 4500Δ/Cr 500Δ None Comparative 3 Au 4500Δ/Cr 500Δ NoneComparative 4 Os 4500Δ/Cr 500Δ None Comparative 5 Ti 5000Δ NoneComparative 6 Ni 4500Δ/Cr 500Δ None Comparative 7 Cr 5000Δ NoneComparative 8 Cu 4500Δ/Cr 500Δ None Comparative 9 Ag 4500Δ/Cr 500Δ NoneComparative 10 Pd 4500Δ/Cr 500Δ None Comparative 11 In 4500Δ/Cr 500ΔNone Comparative 12 Zn 4500Δ/Cr 500Δ None Comparative 13 Mo 4500Δ/Cr500Δ None Comparative 14 Al 5000Δ None Comparative 15  C 4500Δ/Cr 500ΔNone Comparative 16 None ITO 4500Δ/SnO₂ 500Δ Comparative 17 None FTO5000Δ Comparative 18 None ITO 4500Δ/TiO₂ 200Δ Comparative 19 None ITO4500Δ/ZnO₂ 200Δ

TABLE 2 Just After Made One Month Later Example 1 7.9% (◯) 7.5% (◯)Example 2 7.3% (◯) 6.9% (◯) Example 3 6.5% (◯) 6.2% (◯) Example 4 6.4%(◯) 6.2% (◯) Example 5 7.5% (◯) 7.2% (◯) Example 6 7.6% (◯) 7.4% (◯)Example 7 7.3% (◯) 7.0% (◯) Example 8 7.7% (◯) 7.5% (◯) Example 9 7.7%(◯) 7.4% (◯) Example 10 7.5% (◯) 7.0% (◯) Example 11 7.6% (◯) 7.2% (◯)Example 12 7.7% (◯) 7.3% (◯) Example 13 7.2% (◯) 7.1% (◯) Example 147.1% (◯) 6.8% (◯) Example 15 7.5% (◯) 7.1% (◯) Example 16 7.4% (◯) 7.2%(◯) Example 17 7.7% (◯) 7.4% (◯) Example 18 6.2% (◯) 5.9% (◯)Comparative 1 1.5% (◯) 0.2% (Δ) Comparative 2 1.1% (◯) 0.3% (Δ)Comparative 3 1.2% (◯) Inoperative (X) Comparative 4 1.1% (◯) 0.2% (X)Comparative 5 1.3% (◯) 0.2% (Δ) Comparative 6 1.2% (◯) 0.3% (X)Comparative 7 1.1% (◯) Inoperative (X) Comparative 8 1.4% (◯)Inoperative (X) Comparative 9 1.2% (◯) Inoperative (X) Comparative 101.1% (◯) 0.1% (X) Comparative 11 1.3% (◯) 0.1% (X) Comparative 12 1.2%(◯) Inoperative (X) Comparative 13 1.0% (◯) 0.2% (X) Comparative 14 0.5%(◯) Inoperative (X) Comparative 15 0.8% (◯) 0.1% (Δ) Comparative 16 1.5%(-) 1.4% (-) Comparative 17 1.5% (-) 1.4% (-) Comparative 18 0.5% (-)0.4% (-) Comparative 19 0.5% (-) 0.3% (-)Marks in parentheses indicate the following conditions.◯: Good (Unchanged)Δ: Partly dissolvedX: Fully dissolved

EXAMPLE 1

TiO₂ nanoparticles were used as semiconductor nanoparticles. Referringto known methods (H. Arakawa, “Latest Techniques of Dye-sensitized SolarCells” (C.M.C.) p. 45-47 (2001)), paste with dispersed nanoparticles wasprepared as follows. 125 ml of titanium isopropoxide was seeped slowlyinto 750 ml of 0.1M nitric acid water solution while stirring it at theroom temperature. After the seeping, the solution was moved to aconstant temperature bath held at 80° C. and stirred therein for 8hours. Thereby, Thereby, a cloudy, semi-transparent sol solution wasobtained. The sol solution was left to cool down to the roomtemperature, then filtered through a glass filter, and 700 ml thereofwas measured up. The sol solution obtained was moved to an autoclave,then annealed at 220° C. for 12 hours, and thereafter dispersed byultrasonic treatment for one hour. Subsequently, the solution wascondensed by an evaporator at 40° C. until the content of TiO₂ becomes20 wt %. The condensed sol solution was added with polyethylene glycol(having the 500 thousand molecular mass) by 10 wt % relative to theweight of TiO₂ in the paste, and mixed homogenously in a planet ballmill to obtain a viscosity-enhanced TiO₂ paste.

Also prepared was a transparent conductive glass substrate (having thesheet resistance of 1 Ω/□ and sized 30 mm each side) as the transparentsubstrate 1 by stacking in order a 1.1 mm thick substrate of soda limeglass, a 450 nm thick Ru layer as the conductive wiring layer 2 a(wirings 200 μm wide each, with the line-to-line distance of 5 mm on a50 nm thick base), a 450 nm thick ITO layer, and a 50 nm thick SnO₂layer as the metal oxide layer 2 b. The TiO₂ paste already prepared wascoated on the transparent conductive glass substrate by blade coatingover the area of 20 mm×15 mm while making the cap of 200 μm, and held at450° C. for 30 minutes. Thereafter, TiO₂ was sintered on the transparentconductive glass substrate.

After that, the substrate was immersed in a dehydrated ethanol solutionin which 0.5 mM ofcis-bis(isothiocyanate)-N,N-bis(2,2′-dipyridile)-4,4′-dicarboxylicacid)-ruthenium (II) dihydrate and 20 mM of deoxycholic acid for 12hours to have the dye retained. This electrode was washed first byethanol solution of 4-tert-butyl pyridine and next by dehydratedethanol, and dried in a dark place.

The counter electrode used was prepared by sputtering 100 nm thickplatinum on fluorine-doped conductive glass substrate (sheet resistance:10 Ω/□) previously having formed 1 mm sized inlet, then seeping drops ofethanol solution of chloroplatinic acid on the platinum, and heating itto 385° C.

The prepared dye-retained TiO₂ nanoparticle layer, i.e. thesemiconductor electrode, was placed face to face with the platinumsurface of the counter electrode, and their outer circumference wassealed with a 30 μm thick EVA film and epoxy adhesive.

On the other hand, an electrolyte composite was prepared by dissolving0.04 g of lithium iodide (LiI). 0.479 g of 1-propyl-2,3-dimethylimidazolium iodide, 0.0381 g of iodine (I₂) and 0.2 g of 4-tert-butylpyridine into 3 g of methoxypropionitrile.

The above mixed solution was introduced into the device by seeping dropsthereof into the inlet of the device prepared and reducing the pressure,and the inlet was sealed by an EVA film, epoxy adhesive and glasssubstrate. Thus, the photoelectric transfer device was completed.

EXAMPLES 2 TO 18 AND COMPARATIVE EXAMPLES 1 to 19

In Examples 2 to 18, photoelectric transfer devices were prepared in thesame manner as Example 1 except the use of the transparent conductivesubstrate having the conductive wiring layer and the metal oxide layershown in Table 1. In Comparative Examples 1 to 15, photoelectrictransfer devices were prepared in the same manner as Example 1 exceptthe use of the transparent conductive substrate having the conductivewiring layer shown in Table 1 but not having the metal oxide layer. InComparative Examples 16 to 19, photoelectric transfer devices wereprepared in the same manner as Example 1 except the use of thetransparent conductive substrate not having the conductive wiring layer.

With the dye-sensitized wet photoelectric transfer devices according toExamples 1 to 18 and Comparative Examples 1 to 19, photoelectrictransfer efficiency responsive to irradiation of false sunlight (AM 1.5,100 mW/cm²) was measured just after and one month later than fabricationof the devices. Throughout the period of measurement, the photoelectrictransfer devices are exposed to ultraviolet light and held at roomtemperatures.

Conditions of the photoelectric transfer devices were examined by visualobservation.

Results of the measurement are shown in Table 2.

It is appreciated from Table 2 that the dye-sensitized wet photoelectrictransfer devices according to Examples 1 to 18 have been improvedremarkably and much more excellent in durability by the structurestacking the conductive wiring layer 2 a and the metal oxide layer 2 bin comparison with the dye-sensitized wet photoelectric transfer devicesaccording to Comparative Examples 1 to 19 using transparent conductivesubstrates not having conductive wiring layers or metal oxide layers.

Heretofore, an embodiment and practical examples of the presentinvention have been explained. However, the invention is not limited tothese embodiment and practical examples, but contemplates variouschanges and modifications based on the technical concept of theinvention.

Fog example, the numerical values, structures, shapes, materials, sourcematerials, processes, and so on, are mere examples, and any otherappropriate numerical values, structures, shapes, materials, sourcematerials, processes, and so on, may be used, if necessary.

More specifically, although the practical examples immerse the substratealready having the semiconductor nanoparticle layer formed thereon in adye solution to have the dye retained on semiconductor nanoparticles, apaste of semiconductor nanoparticles already retaining the dye may becoated.

As described above, according to the invention, since it uses thetransparent conductive substrate made by stacking the transparentsubstrate, conductive wiring layer and protective layer in order fromthe light-receiving side and having sheet resistance equal to or lessthan 10 Ω/□, it can realize a photoelectric transfer device free fromreverse electron transfer reaction and enhanced in durability andphotoelectric transfer efficiency.

1. A photoelectric transfer device characterized in the use of atransparent conductive substrate made by stacking a transparentsubstrate, a conductive wiring layer and a protective layer in orderfrom the light-receiving side and having sheet resistance equal to orlower than 10 Ω/□.
 2. The photoelectric transfer device according toclaim 1 wherein the protective layer is transparent and electricallyconductive.
 3. The photoelectric transfer device according to claim 1wherein the protective layer is a metal oxide layer.
 4. Thephotoelectric transfer device according to claim 3 wherein the metaloxide layer is made of at least one kind of metal oxides selected fromthe group consisting of In—Sn composite oxides, SnO₂, TiO₂ and ZnO. 5.The photoelectric transfer device according to claim 3 wherein thicknessof the metal oxide layer is in a range from 10 nm to 1000 nm.
 6. Thephotoelectric transfer device according to claim 1 wherein plural linesof the conductive wiring layer are arranged on the transparentconductive substrate, and at least one line of the conductive wiringlayer is connected to a collector portion of the photoelectric transferdevice.
 7. The photoelectric transfer device according to claim 1wherein the conductive wiring layer is made of an electricallyconductive material containing at least an element selected from thegroup consisting of Pt, Au, Ru, Os, Ti, Ni, Cr, Cu, Ag, Pd, In, Zn, Mo,Al and C.
 8. The photoelectric transfer device according to claim 1wherein thickness of the conductive wiring layer is in a range from 50nm to 5000 nm.
 9. The photoelectric transfer device according to claim 1wherein a ratio of area covered by the conductive wiring layer relativeto a light-receiving portion of the photoelectric transfer device is ina range from 0.1% to 20%.
 10. The photoelectric transfer deviceaccording to claim 1 wherein width of each line of the conductive wiringlayer is in a range from 10 μm to 500 μm.
 11. The photoelectric transferdevice according to claim 11 wherein distance between adjacent lines ofthe conductive wiring layer is in a range from 1 mm to 50 mm.
 12. Thephotoelectric transfer device according to claim 1 wherein asemiconductor layer and an electrolyte layer are provided between thetransparent conductive substrate and a conductive substrate as a counterelectrode thereof to generate electrical energy between the transparentconductive substrate and the conductive substrate by photoelectrictransfer.
 13. The photoelectric transfer device according to claim 1wherein the photoelectric transfer device is configured as adye-sensitized wet solar cell.